This invention relates to a flame retardant composition for synthetic fiber substrates and a method of imparting flame resistance to synthetic fiber substrates using the same composition. More particularly, this invention relates to a flame retardant composition suitable for use in imparting flame resistance to polyester, cation-dyeable polyester, polyamide and other synthetic fibers, films, etc., mixtures or blends of such fibers, or composites of such fibers with cellulosic and other fibers other than synthetic fibers, particularly for use in the dye bath addition method (the process for dyeing and imparting flame resistance to a substrate concurrently) and a method of imparting flame resistance to synthetic fiber substrates using the same composition.
It is known, in the art of dip dyeing and thermosol dyeing, to disperse 1, 2, 5, 6, 9, 10-hexabromocyclododecane (hereinafter referred to as HBCD) in water and treat a substrate with the resulting bath to impart flame resistance but this technology has the drawback that the sorption of HBCD into a synthetic fiber substrate is low. Particularly in the dye bath addition system, a large residue of unsorbed HBCD gives rise to mass-like or tarry deposits on the dyeing equipment (hereinafter referred to as the dyeing vessel) etc. which present serious problems by soiling the vessel and the substrate.
Moreover, it is described in Japanese Patent Publication No. 49-24474, No. 49-24475 and No. 50-5187 that depending on the production procedure and conditions used, HBCD occurs as various stereoisomers. While these isomers vary in relative amounts and crystallinity according to different production procedures and conditions, they may be roughly classified into compounds melting at a temperature not less than 195.degree. C. and compounds melting at a temperature below 160.degree. C. These compounds can be produced independently according to the methods described in the above-mentioned patent literature but they occur generally as a mixture when produced by the hitherto-known production procedure. Fractionation of such various stereoisomers can be accomplished by RPC (reversed phase chromatography) or by means of a fractionating solvent having a selective solvent effect on HBCD, for example lower alcohols such as isopropyl alcohol, ethanol, methanol, methylcellosolve, ethylcellosolve, etc. and ketones such as acetone, methyl ethyl ketone, etc. or a mixture of such solvents. A particularly preferred fractionating solvent is a mixture of ethylcellosolve and methanol (weight ratio 1:1).
Though it depends on the degree of purification, the HBCD compound thus fractionated is usually not a single stereoisomer but a mixture of several different stereoisomers and such a mixture (complex) is identified as a compound having a certain melting point. The term `melting point` is used herein to denote such a melting point.
The inventors of this invention conducted a detailed exploration into the influence of such HBCD compounds having different melting points on the dye bath addition process and obtained the following findings.
(1) The sorption of an HBCD compound having a melting point of .gtoreq.195.degree. C. into synthetic fibers such as polyester fiber is only 30 to 50% of that of a compound having a melting point of &lt;160.degree. C.
(2) On the other hand, the sorption of a compound having a melting point of &lt;160.degree. C. into synthetic fibers is 2 to 3 times that of a compound having a melting point of .gtoreq.195.degree. C. However, when the former is used in the dye bath addition system, the unsorbed low-melting compound tends to be left over in the dye bath or entrap the dye to form tarry deposits on the dyeing vessel or the substrate to cause a soiling problem.
(3) When an HBCD compound having a melting point of .gtoreq.195.degree. C. is used in the dye bath addition system, the unsorbed residue, if any, of HBCD does not condense or coagulate but can be easily flushed away from the substrate and dyeing vessel by a simple procedure such as washing with water.
(4) Furthermore, the low-melting HBCD compound (particularly an HBCD compound melting at 130.degree. C. or less) promotes the sorption of an HBCD compound having a melting point of .gtoreq.195.degree. C., which is inherently lower in the rate of sorption into synthetic fibers, into a synthetic fiber substrate (a carrier effect).
This invention has been accomplished based on the above findings.